Inhibiting premature vulcanization of diene rubbers



United States Patent ()flice 3,539,538 Patented Nov. 10, 1970 3,539,538 INHIBITING PREMATURE VULCANIZATION F DIENE RUBBERS Mohammad Behforouz, Charleston, W. Va., assignor to Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed June 5, 1967, Ser. No. 643,401 Int. Cl. C08c 11/54, 11/60 US. Cl. 260-795 19 Claims ABSTRACT OF THE DISCLOSURE New compounds with a nucleus of Ran-ML where the dangling valence on the nitrogen is linked to a second carbonyl, alkyl, aryl, cycloalkyl, hydrogen, alkylene carbon, or arylene carbon and R is alkyl, aryl, or cycloalkyl are inhibitors of premature vulcanization of diene rubbers. Compounds of the formula where x is cycloalkyl, alkyl, aryl, or hydrogen and x is cycloalkyl, alkyl, or aryl; or x and x together with the N atom form a heterocyclic amine; and R is aryl, alkyl, or cycloalkyl are also inhibitors of premature vulcanization of diene rubbers. A combination of a vulcanization accelerator and an inhibitor of this invention is an improved rubber additive which allows longer and safer processing time for rubber.

BACKGROUND OF THE INVENTION The invention pertains to the field of controlled rubber vulcanization art. The applicable US. patent classification defines the invention as retarders.

-In the manufacture of vulcanized rubber products, crude rubber is combined with various other ingredients such as fillers, accelerators, and antidegradants to alter and improve processing of the rubber and to improve the properties of the final product. The crude rubber is put through several steps in the plant before it is ready for the final step of vulcanization. Generally the rubber is mixed with carbon black and other ingredients except the vulcanizing agent and accelerator. Then the vulcanizing and accelerating agents are added to this masterbatch in a Banbury mixer or a mill. Scorching, viz, premature vulcanization, can occur at this stage of the processing, during the storage period before vulcanizing, and during the actual vulcanization. After the vulcanizing and accelerating agents are added, the mixture of crude rubber is ready for calendering or extruding and vulcanization. If premature vulcanization occurs during the storage of the crude mixture or during processing prior to vulcanization, the processing operation cannot be carried out because the scorched rubber is rough and lumpy, consequently, useless. Premature vulcanization is a major problem in the rubber industry and must be prevented in order to allow the rubber mix to be preformed and shaped before it is cured or vulcanized.

There are several reasons oiiered for premature vulcanization. The discovery of the thiazolesulfenamide accelerators constituted a major breakthrough in the vulcanization are because thiazolesulfenamides delayed onset of the vulcanizing process; but, once it started, the built-in amine activation of the thiazole resulted in strong, rapid curing. Mercaptobenzothiazole is a valuable organic vulcanization accelerator but by present standard would be considered scorchy. It has been largely replaced by the delayed-action eccelerators. The development of high pH furnace blacks which lack the inherent inhibiting effect of the acidic channel blacks and the popularity of certain phenylenediamine antidegradants which promote scorching have placed increasingly stringent demands on the accelerator system.

Retarders have long been available to rubber compounders. These include N-nitrosodiphenylamine, salicyclic acid, and a terpene-resin acid blend. See Editors of Rubber World, Compounding Ingredients for Rubber, -128 (3rd Ed., 1965). Acids as retarders are generally inefiective with thiazolesulfenamide accelerators or adversely affect this vulcanizing process. Nitrosoamines as retarders are only of limited eifectiveness with thiazolesulfenamides derived from primary amines. The co-pending application of Joseph E. Kerwood and Aubert Y. Coran, Ser. No. 579,493, filed Sept. 15, 1966, now abandoned in view of continuation-impart application Ser. No. 714,445, filed Mar. 20, 1968, and assigned to Monsanto Company, discloses the use of a class of sulfenamides characterized by the presence of a carbonyl group adjacent to the sulfenamide nitrogen as premature vulcanization inhibitors. The co-pending application of Aubert Y. Coran, Joseph E. Kerwood, and Chester D. Trivette, Ser. No. 518,987, filed Jan. 6, 1966, and assigned to Monsanto Company, discloses the use of sulfenamides of the formula as premature vulcanization inhibitors. The two co-pending applications disclose compounds containing only one sulfur in a sulfenamide linkage as premature vulcanization inhibitors. This invention relates to dithio compounds as premature vulcanization inhibitors.

Himels US. Pat. 2,520,401, Cl. 260293.4 (1950), assigned to Phillips Petroleum Company, discloses dithio compounds obtained from reacting a thiosulfenyl halide with an amine. The compounds disclosed by Himel are useful premature vulcanization inhibitors in this invention.

SUMMARY I have discovered a class of dithio compounds which are inhibitors of premature vulcanization in rubber. The characteristic nucleus is Rs-s-1 I- J- where the dangling valence on the nitrogen may be linked to a second carbonyl, alkyl, aryl, cycloalkyl, hydrogen, alkylene carbon, or arylene carbon and R is alkyl, aryl, or cycloalkyl. Also, compounds of the formula where x is cyloalkyl, alkyl, aryl, or hydrogen and x is cycloalkyl, alkyl, or aryl, or x and x with the nitrogen atom form a heterocyclic amine and R' is aryl, alkyl, or cycloalkyl are also inhibitors of premature vulcanization. Aryl is used in the usual generic sense to mean any univalent organic radical where free valence belongs to an aromatic carbocyclic nucleus and not to a side chain. The term includes radicals substituted in the carbocyclic nucleus, for example, by alkyl, alkoxy, nitro, chloro, bromo, fluoro, iodo, and hydroxy. Alkyl is used in the usual generic sense to mean univalent aliphatic radicals of the series C H2n+1 and includes radicals substituted in the carbon chain, as for example, by aryl, alkoxy, nitro,

9 N- (chlorophenyldithio naphthalimide, N- (benzyldithio naphthalimide, N- (nitrophenyldithio) naphthalimide, N- (n-butyldithio naphthalimide, N- (n-dodecyldithio naphthalimide, N- cyclohexyldithio naphthalimide, N- cyclooctyldithio naphthalimide, N,N'-bis (ar-tolyldithio) -'1,2 ,4,5-benzenetetracarboxylic-1,214,5-diimide, 1,3-bis( cyclohexyldithio -2-imidazolidinone, 1,3 -bis (cyclooctyldithio) -2-imidazolidinone, 1,3-bis (phenyldithio -2-imidazolidinone, 1,3-bis (chlorophenyldithio -2-imidazolidinone, 1 ,3 -bis (benzyldithio -2-imid azolidinone, 1,3-bis(tolyldithio -2-irnidazolidinone, 1,3-bis (nitrophenyldithio -2-imidazolidinone, 1,3-bis (t-butyldithio) -2-imida.zolidinone, 1,3 -b is methyldithio -2-imidazolidinone, 1,3-bis (cthyldithio -2-imidazolidinone, 1,3-bis (propyldithio -2-imidazolidinone, 1, 3 -bis (isopropyldithio -2-imidazolidinone, 1,3-bis (n-dodecyldithio -2-imidazolidinone, 1- (n-dodecyldithio -2-imidazolidinone, 1-cyclohexylthio-3 -cyclohexyldithio-2-imidaz olidinone, 1-cyclooctylthio-3-cyclooctyldithio-Z-imidazolidinone, 1-phenylthio-3 -phenyldithio-2-imidazolidinone, 1-chlorophenylthio-3 -chlorophenyldithio-2-imidazolidinone 1-benzylthio-3 -benzyldithio-2-imidazolidinone, 1-tolylthio-3-tolyldithio-2-irnid azolidinone, 1-nitrophenylthio-3-nitrophenyldithio-2-imidazolidinone, 1-t-butylthio-3-t-butyldithio-2-imidazolidinone, 1-methylthio-3 -methyldithio-2-imidazolidinone, 1-ethylthio-3-ethyldithio-2-imidazolidinone, 1-propylthio-3 -propyldithio-2-imidazolidinone, 1-n-dodecylthio-3-n-dodecyldithio-2-imidazolidinone, N-[ (trichloromethyl dithio] succinimide, N- (n-butyldithio) succinimide, N- (methyldithio succinimide, N- ethyldithio succinimide, N- (propyldithio) succinirnide, N- isopropyldithio succinimide, N'( cyclohexyldithio succinimide, N- (cyclooctyldithio) succinimide, N- p-chlorophenyldithio succinimide, N- o-tolyldithio) succinimide, N- (m-tolyldithio succinimide, N- (p-tolyldithio) succinimide, N- t-butyldithio) succinimide, N- phenyldithio succinimide, N-(nitrophenyldithio) succinimide, N- n-dodecyldithio) succinimide, and N- (benzyldithio succinimide.

Other compounds which are useful in the practice of this invention are N- (phenyldithio) morpholine, N- phenyldithio -2,6-dimethylmorpholine, N- (phenyldithio dicyclohexylamine, N-( phenyldithio aniline, N- (phenyldithio diisopropylamine, N- (phenyldithio) diethyla rnine, N- (phenyldithio t-butylamine, N,N'-bis (phenyldithio) ethylenediarnine, N- phenyldithio -N-pheny1-ethylamine, N- phenyldithio) cyclohexylamine, N-phenyldithio-N-t-butyl-ethylamine, N-phenyldithio-N-cyclohexylmethylamine, N-phenyldithio-N-phenylethylamine, N-phenyldithi-N-phenyl-cyclohexylamine, N-tolyldithio-N-cyclohexyl-methylamine, N (n-butyldithio) morpholine, N- benzyldithio) morpholine, 1,4-bis (n-butyldithio piperazine, N- (dodecyldithio morpholine, 1,4 bis (benzyldithio piperazine,

1 0 N- t-butyldithio morpholine, N- n-butyldithio -N-ethyl-n-butylamine, N (n-butyldithio-N-methylaniline, N- (n-octyldithio )morpholine, 1,4-b-is (decyldithio piperazine, N- (n-tetradecyldithio) morpholine, 1,4-bis (n-hexadecyldithio piperazine, N- n-octadecyldithio morpholine, N- sec-tridecyldithio morpholine, N-( sec-octyldithio )morpholine, 1,4-bis t-pentadecyldithio piperazine, N- isobutyldithio morpholine, N- (phenyldithio) piperidine, N- (cyclohexyldithio piperidine, and N- isobutyldithio piperidine.

Rubber stocks containing delayed-action accelerators can be used in the process of this invention. Cheaper, more scorchy accelerators can also be used. The improved vulcanizing process of this invention can be used advantageously to process stocks containing furnace blacks as well as stocks containing other types of blacks and fillers used in rubber compounding. The invention is also applicable to gum stocks.

My invention is applicable to rubber mixes containing sulfur-vulcanizing agents, peroxide-vulcanizing agents, organic accelerators for vulcanization, and antidegradants. For the purposes of this invention, sulfur-vulcanizing agent means elemental sulfur or sulfur-containing vulcanizing agent. The invention is applicable to rubber mixes containing vulcanization accelerators of various classes. For example, rubber mixes containing the aro matic thiazole accelerators which include benzothiazyl-Z- monocyclohexyl sulfenamide, Z-mercaptobenzothiazole, N-t-butyl-2-benzothiazole sulfenamide, 2-benzothiazolyl diethyldithiocarbamate, and 2-(morpholinothio)benzothiazole can be used. Amine salts of marcaptobenzothiazole accelerators, for example, the t-butylamine salt of mercaptobenzothiazole, like salts of morpholine and 2,6- dimethylmorpholine, can be used in the invention. Thiazole accelerators other than aromatic can be used. Stocks containing accelerators, for example, the tetramethylthiuram disulfide, tetramethylthiuram monosulfide, aldehydeamine condensation products, thiocarba-mylsulfenamides, thioureas, xanthates, and tguanidine derivatives, are substantially improved using the process of this invention. Examples of thiocarbamylsulfenamide accelerators are shown in US. Pats. 2,381,392, Aug. 7, 1945, Smith assigned to Firestone; 2,388,236, Nov. 6, 1945, Cooper assigned to Monsanto; 2,424,921, July 29, 1947, Smith assigned to Firestone; and British Pat. 880,912, Oct. 25, 1961, Dadson assigned to Imperial Chemical Industries Limited. The invention is applicable to accelerator mixtures. The invention is applicable to stocks containing amine antidegradants. Rubber mixes containing antidegradants, for example, -N-1,3-dimethylbutyl-N-phenyl-pphenylenediamine, N,N'-bis( 1 ,4-dimethylpentyl) -p-phcnylenediamine, and other phenylenediamines, ketone, ether, and hydroxy antidegradants, and mixtures thereof, are substantially improved using the process of my invention. Mixtures of antidegradants, for example, a mixture of N 1,3 dimethylbutyl-N'-phenyl-p-phenylenediamine and N,N'-bis(1,4-dimethylpentyl) p phenylenediamine, furnish a much improved final product when used with the inhibitors of this invention.

The inhibitors of this invention can be used in natural and synthetic rubbers and mixtures thereof. Synthetic rubbers that can be improved by the process of this invention include cis-4-polybutadiene, butyl rubber, ethylenepropylene terpolymers, polymers of 1,3-butadiene, for example 1,3-butadiene itself and of isoprene, copolymers of 1,3-butadiene with other monomers, for example, styrene, acrylonitrile, or isobutylene, and methyl methacrylate. The invention relates to diene rubbers and the terms, rubber and diene rubber, are synonymous for purpose of this invention.

1 1 The new compounds of this invention are prepared in the following manner:

N-(phenyldithio)phthalimide is synthesized according to the following equations:

n-pentane Et N'HOl To prepare N-(phenyldithio)phthalimide, 51.5 grams (0.5 mole) of sulfur dichloride is dissolved in 500 ml. of n-pentane in a l-liter three-necked flask equipped with a mechanical stirrer, a condenser, and a dropping funnel. Then a solution of 55 grams (0.5 mole) of thiophenol in 50 ml. of n-pentane is added dropwise to the flask contents at 77 to 50 C. over a period of 90 minutes. The flask contents are then added to a solution of 73.5 grams (0.5 mole) of phthalimide, and 65.0 grams (0.5 mole) of triethylamine in 300 ml. of dimethylformamide; and the reaction mixture is stirred for two hours. Two liters of cold water are added to the reaction mixture, the mixture is stirred, and the resulting solid is filtered and dried. An 89% yield is obtained weighing 127.0 grams. A sample of the product is recrystallized from a mixture of 50 parts by volume of methanol and 50 parts ethyl acetate to give a white solid, melting point 143 -l45 C. Analysis of the product shows 4.48% nitrogen and 22.05% sulfur. Calculated percentages for C H NO S are 4.87% nitrogen and 22.31% sulfur. The infrared spectrum is consistent with the structure of N-(phenyldithio) phthalimide.

To prepare N-(t-octyldithio)phthalimide, 58.0 grams (0.2 mole) of t-dioctyldisulfide is dissolved in 600 ml. of isopentane in a 1-liter three-necked flask equipped with a mechanical stirrer, a condenser, and a gas inlet tube. Then chlorine gas is passed into the solution at 45 to 48 C. over a period of 25 minutes. The amount of chlorine used is 14.5 grams (0.2 mole). The flask contents are then added to a solution of 29.4 grams (0.2 mole) of phthalimide and 27.0 grams (0.27 mole) of triethylamine in 195 ml. of dimethylformamide over a period of minutes at C. The reaction mixture is stirred until the reaction temperature reaches room temperature. The reaction mixture is transferred to a three-liter beaker and 2.5 liters of ice water are added. The mixture is stirred, and the resulting soft-solid product is filtered. A quantitative yield is obtained. A sample of the product is recrystallized from n-heptane, and a white solid with a melting point of 75 C. is obtained. Analysis of the product shows 4.4% nitrogen and 19.82% sulfur. Calculated percentages for C I-I NO S are 4.3% nitrogen and 19.82% sulfur. The infrared spectrum is consistent with the structure of N-(toctyldithio phthalimide.

To prepare N-(cyclohexyldithio)phthalimide, 21 grams (0.2 mole) of sulfur dichloride is dissolved in 100 ml.

of methylene chloride in a 1-liter three-necked flask equipped with a mechanical stirrer, a condenser, and a dropping funnel. To this solution of 29.4 grams (0.2 mole) of phthalimide and 20.0 grams (0.2 mole) of triethylamine is added dropwise at 10 to '+3 C. over a period of one hour. A solution of 23.2 grams (0.2 mole) of cyclohexylmercaptan and 25.0 grams (0.25 mole) of triethylamine in 50 ml. of methylene chloride is added to the reaction mixture over a 30 minute period of 0 to 5 C. The reaction mixture is stirred for one hour, then 200 ml. of water are added to it, and the organic layer is separated. The organic layer is evaporated to give a thick pasty brown product. About 150 ml. of n-heptane are added to the product and it is warmed, then cooled, by a Dry-Ice acetone bath and filtered. A 73% yield, 42.4 grams, of a brown product is obtained. Recrystallization of a sample of the product from n-heptane gives a white solid with a melting point of 74 to 77 C. Analysis of the product shows 4.37% nitrogen and 22.3% sulfur. Calculated percentages for C H NO S are 4.7% nitrogen and 21.8% sulfur. The infrared spectrum is consistent with the structure of N-(cyclohexyldithio) phthalimide.

To prepare N-(n-propyldithio)phthalimide, 2.10 grams of sulfur dichloride are dissolved in ml. of n-pentane in a 250 ml. of three-necked flask equipped with a mechanical stirrer, a condenser, and a gas inlet tube. Then 15.2 grams (0.2 mole) of n-propyl mercaptan in 75 ml. of n-pentane are added over a period of 35 minutes at 68" to -72 C. The solution is transferred to a 500 ml. round-bottomed flask, and the hydrogen chloride is removed under a vacuum. The vacuumed solution is added dropwise to a solution of 29.4 grams (0.2 mole) of phthalimide and 30 grams (0.3 mole) of triethylamine in ml. of dimethylformamide at 10 to 15 C. over a 50 minute period. The reaction mixture is stirred for 2 hours, then two liters of ice water are added and stirred, and the oily layer is separated. The solution is extracted twice with ether, and the ether solution is added to the organic phase separated previously. The organic phase is evaporated and dried to give 42.0 grams, a 95% yield, of a red liquid. The 42.0 grams of red liquid are dissolved in n-heptane and cooled in a Dry-Ice acetone bath to yield a solid product. Recrystallization of a sample of the product gives a white solid with a melting point of 35 to 38 C. Analysis of the product shows 5.30% nitrogen and 25.35% sulfur. Calculated percentages for C H NO S are 5.53% nitrogen and 25.31% sulfur. The infrared spectrum is consistent with the structure of N-(n-propyldithio)phthalimide.

To prepare N-(isobutyldithio)succinimide, 45.0 grams (0.5 mole) of isobutyl mercaptan is dissolved in 50 ml. of n-pentane and then added to a solution of 51.5 grams (0.5 mole) of sulfur dichloride in 250 ml. of n-pentane at 75 to 65 C. over a 30 minute period in a 500 ml. three-necked flask equipped with a mechanical stirrer, a condenser, and a dropping funnel. The solution is stirred during this period. The resulting solution is then added dropwise to a 1-liter three-necked flask equipped with a mechanical stirrer, a condenser, and a dropping funnel and containing 37.5 grams (0.5 mole) of succinimide and 70.0 grams (0.70 mole) of triethylamine in 250 ml. of dimethylformamide. The reaction mixture is stirred for 30 minutes and then transferred to a beaker. One liter of cold water is added, the organic layer is separated, dried over sodium sulfate, and evaporated to give 70.0 grams, a 63% yield, of a brown liquid. The infrared spectrum is consistent with the structure of N-(isobutyldithio)succinimide. The remaining compounds of this invention are prepared in a similar manner to the preparations described above with comparable results.

The following tables illustrate the utility of the invention. For the rubber stocks tested and described, infra, as illustrative of the invention, Mooney scorch times at 121 13 C. and 135 C. are determined by means of a Mooney plastometer. The time in minutes (2 required for the Mooney reading to rise five points above the minimum viscosity is recorded. Longer times are indicative of the activity of the inhibitor. Longer times on the Mooney Scorch Test are desirable because this indicates greater processing safety. Percentage increases in scorch delay are calculated by dividing the Mooney scorch time of the stock containing the premature vulcanization inhibitor by the Mooney scorch time of the control stock, multiplying by 100, and subtracting 100. These increases show the per- 14 which contains no premature vulcanization inhibitor. The stocks in Tables I, II, and III contain the following:

Parts by weight Natural rubber 100 Carbon black 45 5 Zinc oxide 3 Stearic acid 2 Hydrocarbon softener 5 Sulfur 2.5 Santocure MOR 0.5 Santoflex 13 2 TABLE I Percent Mooney increase Rheometer at 144 C. scorch at in scorch Premature vulcanization inhibitor C./t5 delay t2 t R.M.T. k2

25.7 8.0 22.5 59.0 0.157 N-(t-octyldithio)-phthalimide (1 part by Weight) 53. 2 107 15.0 30. 0 57. 8 0. 162

centage improvement in scorch delay over the control stock which contains no inhibitor. Additionally, cure ratings are calculated from the time required to cure the stocks at 144 C., and in some cases 153 C. Curing characteristics are determined by means of the Monsanto Oscillating Disk Rheometer described by Decker, Wise, and Guerry in Rubber World, December 1962, page 68. From the Rheometer data, R.M.T. is the maximum torque The data in Table II illustrate the results using inhibitors of this invention in natural rubber stocks containing other additives routinely used in rubber. The k values illustrate a faster cure rate for rubber stocks including the premature vulcanization inhibitors, N-(isobutyldithio)succinimide, N-(isobutyldithio)piperidine, N-(phenyldithio)- morpholine, and N-(isobutyldithio)morpholine, of this invention compared to the control.

TABLE II Percent Mooney Cure increase Rheometer at 144 C. scorch at rate in scorch Premature vulcanization inhibitor 1 1 C./t5 tarts delay tr tan R.M '1 k 33. .5 11.8 27.5 51.5 0.155 N-(phenyldithio)phthalimide (1 part by Weight)- 50. 1 6. 3 31 14. 0 31. 3 54. 8 0.155 N (isobutyldithio)-succinimit1e (0.5 part by Weight 49. 4 5. 5 29 1 1. 5 30. 5 53. 0 0. 162 N-(isobutyldithio) piperidine (1 part by Weight) 40. 3 3. 6 5. 5 12. 5 25. 5 65.6 0. 198 N-(phenyldithio)-morpho1ine (1 part by Weight)- 21. 6 5. l 8. 0 12. 8 27. 0 58. 0 0. 19 N-(isobutyldithio) -rnorpholine (1 part by \Velght 47. O 5. 3 24 13. 8 26. 8 63. O O. 21

in Rheometer units, 1 is the time in minutes for a rise of two Rheometer units above the minimum reading, and I is the time required to obtain a torque 90% of the maximum. The specific rate constant k is measured in reciprocal minutes and is described by Coran in 37 Rubber Chemistry and Technology, 689, (1964). Higher values of k indicate higher rates of cross-linking in rubber.

Santocure MOR and Santoflex 13 in the tables, infra, are trademarks. Santocure MOR is a trademark for the The data in Table III illustrate the results obtained using N-(cyclohexyldithio)phthalimide and N-(n-propyldithio)phthalimide as premature vulcanization inhibitors in stocks of natural rubber containing other additives routinely used in rubber. The rubber stocks using the premature vulcanization inhibitors of this invention show an increase in maximum torque with an increase in inhibitor concentration. The stocks include the following concentrations of premature vulcanization inhibitors:

accelerator 2 (morpohlinothio)benzothiazole. Santoflex 13 is a trademark for the antidegradant N-l,3-dimethyl- Fags 'r e y -pr y Stock Inhibitor weigh The data 111 Table I illustrate the results obtained using 1 N Inhm Nt -p yl )p as a premature vulcanizati0n 213:: N 2eyioiigiynanugs555155 5.; "I "629 inhibitor in a natural rubber stock containing other adg-gg l g lg gg gp gg l m gm 15$ ditives routinely used in rubber. The second stock which j: I $23 ,515.g fg yg gf contains the N-(t-octyldithio)phthalimide of this invention mj py g g )pfi g fi l mg m 1 shows a 107% increase in scorch time over the first stock i mpy 1 10)) a e TABLE III Stock 1 2 3 4 5 6 7 Mooney scorch at 121 0.:

t5 24.2 35.2 41.7 52.1 33.9 40.0 49.7 tea-D 6.1 6.4 7.0 9.1 6.5 7.4 7.7 Percent increase in scorch delay 45 72 115 40 Rheometer at 144 C.:

n 12. 5 15. 0 11.0 12. 0 14. 5 25. 3 2s. 0 22. 6 24. 0 23. 9 5s. 1 53. 3 5s. 3 5s. 7 59. 0 0. 173 0. 168 0. 173 0.164 0.168

1 5 Table IV illustrates the results obtained using N-(thexyldithio)phthalimide as a premature vulcanization inhibitor in an oil-extended styrene-butadiene rubber. The stocks in Table IV contain the following:

Parts by weight Oil-extended styrene-butadiene rubber containing Comparable results to those in the tables, supra, are obtained using other compounds of this invention as premature vulcanization inhibitors.

It is intended to cover all changes and modifications of the examples of the invention herein chosen for purposes of disclosure which do not constitute departures from the spirit and scope of the invention.

I claim:

1. A vulcanizable composition comprising diene rubber, vulcanizing agent, an organic vulcanization accelerating agent, and an amount effective to inhibit premature vulcanization of a compound selected from the group consisting of wherein the dangling valence on the nitrogen is linked to a second carbonyl, lower alkyl, lower cycloalkyl, aryl of the phenyl or naphthyl series, hydrogen, lower alkylene, a divalent unsaturated radical derived by removing two hydrogen atoms from lower alkylene, or arylene of the phenylene or naphthylene series, with the proviso that when the dangling valence of the nitrogen is linked to carbonyl, the valences of the two carbonyls are satisfied by arylene of the phenylene or naphthylene series, lower alkylene, a divalent unsaturated radical derived by removing two hydrogen atoms from lower alkylene, nitrogen and carbon forming a hydantoin ring, hydrogenated arylene of the phenylene or naphthylene series, or a divalent 7 member bicyclo radical; when the dangling valence of the nitrogen is linked to lower alkylene, a divalent unsaturated radical derived by removing two hydrogen atoms from lower alkylene, or arylene of the phenylene or naphthylene series, the remaining valence and the valence of the carbonyl are satisfied by NH--; when the dangling valence of the nitrogen is linked to a monovalent radical, the valence of the carbonyl is satisfied by N-arylamino, N-lower cycloalkylamino, N-lower cycloalkylthioamino, N-lower alkylthioamino, N-aryldithioamino, N-lower cycloalkyldithioamino, or N-lower alkyldithioamino where aryl is of the phenyl or naphthyl series and R is lower alkyl, lower cycloalkyl or aryl of the phenyl or naphthyl series; and

wherein x is lower cycloalkyl, lower alkyl, aryl of the phenyl or naphthyl series, or hydrogen and x is lower cycloalkyl, lower alkyl, or aryl of the phenyl or naphthyl series, or x and x together with the nitrogen atom are morpholine, lower alkyl substituted morpholine, or

piperidine, and R' is aryl of the phenyl or naphthyl series,

lower alkyl, or lower cycloalkyl.

2. A composition of claim 1 wherein the vulcanizing agent is a sulfur-vulcanizing agent.

3. A vulcanizable composition comprising diene rubber, sulfur, an organic vulcanization accelerating agent, and an amount efiective to inhibit premature vulcanization of a compound selected from the group consisting of wherein R and R with the carbonyl and N atom are N-phthalimidyl, N-succinimidyl, 1,4,5,6,7,7-hexachlorobicyclo[2.2.1]hept-5-ene 2,3 dicarboximid-N-yl, 5,5-dimethyl-3-hydantoinyl, 5,5-diphenyl 3 hydantoinyl, N- maleimidyl, N-adipimidyl, N-glutarimidyl, N-malonimidyl, N-hexahydrophthalimidyl, 7-oxoabicyclo[2.2.l]heptame-2,3-dicarboXimid-N-yl, 7 oxabicyclo[2.2.1]hept-5- one-2,3-dicarboXimid-N-yl, tetrapnopenylsuccinimid-N-yl, methylsuccinimid-N-yl, octadecylsuccinimid-N-yl, n-decenylsuccinimid-N-yl, 4 cyclohexene-1,2-dicarboximid-N- yl, Z-benzimidazolinon-l-yl, 2-benzothiazolinon-N-yl( 3- arylthio-2 benzimidazolinon-l-yl, 3-alkylthio-2-benzimidazolinon-l-yl, 3-cycloalkylthio-2-benzimidazolin-on1-yl, 3- aryldithio-Z-benzimidazolinon-1-yl, 3 alkyldithio-Z-benzimidazolinon-l-yl, 3-cycloalkyldithio-2-benzimidazolinonl-yl, 2-imidazolidinon-1-yl, 3-arylthio-2-imidazolidinon-1- yl, 3-alkylthio-2-imidazolidinon-l-yl, 3-cycloalkylthio-2- imidazolidinon-l-yl, 3-aryldithio-2-imidazolidinon-l-yl, 3- alkyldithio-2-imidazolidinon 1 yl, 3-cycl0alkyldithio-2- imidazolidinon-l-yl, 2 imidazolinon-l-yl, 3-arylthio-2- imidazolinon-l-yl, 3 cycloalkylthio-Z-imidazolinon-1-yl, 3-aryldithio-2-imidazolinon-1-yl, 3-alkyldithio-2-imidazolinon-l-yl, 3-alkyldithio-2-imidazolinon-1yl, 3-cycloalkyldithio-Z-imidazolinon-1-yl, bicyclo[2.2.1]hept-5-ene-2,3- dicarboximid-N-yl, alkylbicyclo[2.2.l]hept-5 ene-2,3-dicarboximid-N-yl, N-(arylthio) 1,2,4,5 benzenetetracarboxylic-l,2:4,5-diimid-N'-yl, N (cycloalkylthio)-1,2,4,5- benzenetetracarboxylic 1,2:4,5 diimid-N-yl, N-(alkylthio) 1,2,4,5 benzenetetracarboxylic-1,2:4,5-diimid-N- yl, N- (aryldithio) -1,2,4,S-benzenetetracarboxylic-1,2 4,5 diimid-N-yl,N-(alkyldithio) 1,2,4,5 benzenetetracarboxylic-1,2:4,5-diimid-N'-yl, N-(cycloalkyldithio)-1,2,4,5- benzenetetracarboxylic-1,2:4,5-diimid-N'-yl, N naphthalimidyl, or N-(3,4,5,6-tetrahalophthalirnidyl),

and

R" is aryl of the phenyl or naphthyl series, lower cycloalkyl, or lower alkyl;

III

(b) R-C-N-S-S-R' morpholine, lower alkyl substituted morph-oline, or piperidine, and

R is aryl of the phenyl or naphthyl series, lower alkyl,

or lower cycloalkyl.

4. A composition of claim 3 wherein the accelerating agent is a thiazole accelerator.

5. A composition of claim 3 whereinthe inhibitor is N- (is obutyldithio) succinimide.

6. A composition of claim 3 wherein the accelerating agent is a thiazole sulfenamide.

7. A composition of claim 3 wherein the inhibitor is 1,3 -bis (phenyldithio) -2-benzimidazolinone.

8. A composition of claim 3 whereint he inhibitor is N- (pheny1dithio)morpholine.

9. A composition of claim 3 wherein the inhibitor is N- (phenyldithio )phthalimide.

10. A composition of claim 3 wherein the rubber is natural rubber.

11. A compisition of claim 3 wherein the inhibitor is N- (cyclohexyldithio )phthalimide.

12. A composition of claim 3 wherein the rubber is styrene-butadiene rubber.

13. A composition of claim 3 wherein the inhibitor is N- (t-octyldithio phthalimide.

14. An accelerator-inhibitor combination for rubber compounding comprised of an organic vulcanization accelerating agent and a compound, in an amount effective to inhibit premature vulcanization of a vulcanizable diene rubber, selected from the group consisting of wherein R and R with the carbonyl and N atom are N-phthalimidyl,

N succinimidyl,

1,4,5 ,6,7 ,7 -hexachlorobicyclo [2.2. 1 hept-S -ene-2,3-

dicarboXimid-N-yl,

5,5-dimethyl-3-hydantoinyl,

5,5-diphenyl-3-hydantoinyl,

N-maleimidyl,

N-adipirnidyl,

N-glutarimidyl,

N-malonimidyl,

N-hexahydrophthalimidyl,

7-oxabicyclo[2.2.1] heptane-2,S-dicarboximid-N-yl,

7-oxabicyclo[2.2.1]hept-5-ene-2,3 -dicarboximid-N-yl,

tetrapropenylsuccinimid-N-yl,

methylsuccinimid-N-yl,

octadecylsuccinimid-N-yl,

n-decenylsuccinimid-N-yl,

4-cyclohexene-1,2-dicarboximid-N-yl,

2-benzimidabolinon-1-yl,

Z-benzothiazolinon-N-yl,

3-arylthio-2-benzimidazolinon-l-yl,

3-a1kylthio-2-benzimidazolinon-l-yl,

3-cycloalkylthio-2-benzimidazolinon-l-yl,

3-aryldithio-2-benzimidazolinon-l-yl,

3-alkyldithio-2-benzimidazolinon-l-yl,

3-cycloa1kyldithio-Z-benzimidazoliuon-l-yl,

2-imidazolidinon-1-yl,

3-arylthio-Z-imidazolidinon-l-yl,

3-alkylthio-2-imidazolidinon-l-yl,

3-cycloalkylthio-2-imidiazolidinon-1-yl,

3-aryldithio-Z-imidazolidinon-l-yl,

3-alkyldithio-2-imidazolidinon-l-yl,

2-imidazolinon-1-yl,

3 -arylthio-2-imidazolinonl-yl,

3-alkylthio-2-imidazolinonl-yl,

3 -cycloalkylthio-Z-imidazolinon- 1 -y1,

3 -aryldithio-2-imidazolinonl-yl,

3-alkyldithio-2-imidazolinonl-yl,

3 -cycloalkyldithio-Z-imidazolinonl-yl,

bicyclo [2.2. l hept-5-ene-2,3-dicarboximid-N-yl,

alkylbicyclo [2.2.1 ]hept-5-ene-2,3-dicarboximid-N-yl,

N- (arylthio 1 ,2,4,5 -benzenetetracarboxylic-1 ,2 4,5

diimid-N'-yl,

N-(cycloalkylthio)-1,2,4,5-benezenetetracarboxy1ie- 1,2 4,5-diimid-N'-yl,

N- (alkylthio -1,4,S-benzenetetracarboxylic-1,2:4,5-

diimid-N'-yl,

N-(aryldithio) -1,2,4,S-benzenetetracarboxylic-l,2:4,5-

diimid-N'-yl,

N-(alkyldithio) -l,2,4,S-benzenetetracarboxylic-1,2: 4,5-

diimid-N'-yl,

N-(cycloalkyldithio)-1,2,4,S-benzenetetracarboxylic- 1,2 4,5 -diimid-N'-yl,

N-naphthalimidyl, or

N- (3 ,4,5,6-tetrahalopthalimidyl) and R is aryl of the phenyl or naphthyl series, lower cycloalkyl, or lower alkyl;

5 N- arylthio carbamoyl,

N- (lower alkylthio) -carbamoyl, N-(lower cycloalkylthio)-carbamoyl, N- (aryldithio) -carbamoyl,

N-(lower alkyldithio)-carbamoyl, N-(lower cycloalkyldithio)-carbamoyl, N-arylcarbamoyl,

N-lower alkylcarbamoyl, or

N-lower cycloalkylcarbamoyl where aryl is of the phenyl or naphthyl series, and

R' is lower alkyl, lower cycloalkyl, or aryl of the phenyl or naphthyl series; or

wherein x is lower cycloalkyl, lower alkyl, aryl of the phenyl or naphthyl series, or hydrogen, and x is lower cycloalkyl, lower alkyl, or aryl of the phenyl or naphthyl series, or

x and x together with the nitrogen atom are 1 9 20 18. An accelerator-inhibitor combination according to 3,008,936 11/1961 Karnlet 26083.3 claim 14 wherein the accelerator is a sulfenamide accelera- 3,427,319 2/ 1969 Coran et a1 260 3 09.2

tor and the inhibitor is N-(t-octyldithio)phthalimide.

19. An accelerator-inhibitor combination according to FOREIGN PATENTS claim 14 wherein the accelerator is a sulfenamide accelera- 5 79 4/ 195 8 r at Britain.

tor and the inhibitor is N-(phenyldithio)morpholine.

DONALD E. CZAJ A, Primary Examiner References Cited R. A. WHITE, Assistant Examiner I UNITED STATES PATENTS 1,904,934 4/1933 Sibley 260780 10 2,264,758 12/1941 Jones 260 780 252-402, 260-780 2,727,014 12/1955 Harbison 260-415 

